1. Field of the Invention
This invention relates in general to the construction of exhaust gas treatment devices and in particular to a new and useful device for the catalytic purification of exhaust gases and to an improved structure therefor.
2. Description of the Prior Art
The present invention relates to a device for the catalytic purification of exhaust gases of internal combustion engines, in which the monolithic catalyzer is received in a housing. Such devices are already known. For example, a known construction includes an arrangement in which the catalyst body is provided with an external protective envelope of a fibrous aluminum silicate and supported, along with this protective envelope, on the inner surface of the housing, through an elastic, corrugated part. Frontally, in the flow direction, the catalyst body is retained by inwardly extending annular housing flanges. Another known arrangement is a device in which the catalyst body is received in a double-walled housing having elastic elements disposed between the two walls and is frontally fixed by rings made of a soft elastic, noncombustible material. Here, it is intended to support the catalyst body within a housing so as to enable it to withstand for a long time even extreme shock stresses due to the pulsation of the exhaust gas and to forces acting from the outside. In the known arrangements, the catalyst bodies have a relatively low mechanical resistance because of their thin-walled rib structure and are sensitive to stresses caused by rapidly varying temperatures. Now, the coefficient of thermal expansion of the conventional catalyst bodies is notably smaller than the coefficient of expansion of the supporting parts which are made of metal alloys such as Fe-Ni-Cr.
This means that at the high temperatures occurring during operation and being of the order of 850.degree. C, relative deviations appear between the catalyst body and the supporting parts which, in the arrangements known up to date, are of the order of 1 mm. Howevr, under all operational circumstances, it must be insured that a force closure is continuously maintained between supports and catalyst body, i.e. the catalyst body must not move in its mounting. This requirement applies both to the axial and radial support. In some of the known solutions, rings of soft elastic materials are provided for compensating the unequal thermal expansions.
It has been found that the elastic deformation the rings can be credited with is very limited. The same problem, i.e. to insure an increased travel of the elastic system at the occurring temperatures and with economically acceptable expenses, arises at the use of other elastic mounting elements such as cup springs and metal bellows.